1. Field of the Invention
This invention relates to a card reader/writer for supplying data, etc. to a non-contact type data record medium, such as a non-contact type IC card, etc., in a non-contact manner by magnetic coupling, and more particularly to a magnetic coupling circuit-driving system for driving a magnetic coupling circuit incorporated in the card reader/writer.
2. Description of the Related Art
To enhance the reliability of an IC card as a data record medium, a non-contact type IC card and its card reader/writer (hereinafter referred to simply as "IC card" and "reader/writer", respectively) have recently been developed, which have no electric contacts therebetween and transmit power, data, etc. in a non-contact manner by magnetic coupling. When the IC card having two coupling coils and the reader/writer have been set, two coils constituting a magnetic coupling circuit in the reader/writer are magnetically coupled with the two coils of the IC card, thereby transmitting data in a non-contact manner through a magnetic field modulated on the basis of a PSK (Phase Shift Keying) modulation system.
In general, the two coils which constitute the magnetic coupling circuit of the reader/writer are simultaneously excited by two power signals which have a predetermined amplitude and a phase difference of 90.degree. therebetween. Then, these two coils generate two magnetic fields with a phase difference of 90.degree., thereby generating a carrier wave to the IC card in a non-contact manner to supply thereto power, data, a clock signal, etc.
When the carrier wave is received by the IC card, it will be adversely influenced by the magnetically-coupled two coils of the IC card, since these coils are located close to each other in the IC card. In the conventional system, to prevent a turbulence in the magnetic field due to the influence and supply a signal of a predetermined voltage amplitude to the two coils of the IC card, the two coils of the reader/writer must be simultaneously driven by a power signal of a high voltage amplitude. Thus, the system requires high driving power, i.e. it costs high.